Fe(IV)═O/Fe(V)═O and [Fe_aq^IVO]²⁺/[Fe_aq^VO]³⁺ Cooperating with Free Radicals Induced High-Rate Sulfamethoxazole-Cr(VI) Simultaneous Removal in a Fe₇S₈-Persulfate Micro/Nanocatalytic System

Abstract

Conventional persulfate-based (PS-based) catalytic systems that resolve single-pollutant sulfamethoxazole (SMX) problems depend on free radicals. However, research on the contribution or cooperative effect of nonfree radical Fe(IV)/Fe(V) species and the interaction of cocontamination Cr(VI)-SMX has not been sufficiently elucidated. The production source of the Fe(IV)/ Fe(V) species requires further exploration and expansion. Here, a pyrrhotite-PS (Fe 7 S 8 -PS) micro/nanocatalytic system was independently constructed to stimulate the production of Fe(IV)/Fe(V) species, which were identified by Mossbauer spectroscopy. In the Fe(IV)/Fe(V) species cooperating with the freeradical-induced high-rate reaction system, k SMX (0.0304 min −1 ) raised 152.0 times to k SMX (0.0002 min −1 ) in the sole Fe 7 S 8 system. SMX has five possible degradation pathways in which the fractures of the S−N and N−C bonds are the two main chain scission degradation pathways confirmed through density functional theory (DFT) calculations. Furthermore, Cr(VI) was dominated by rapid reduction (0.0227 min −1 ) to low-toxicity Cr(III), which was eventually adsorbed by the dynamically transformed Fe 7 S 8 and secondary iron-oxide minerals. The SMX reaction path and degradation rate were increased by [Fe aqIV O] 2+ /[Fe aq V O] 3+ in the solution (reacting with SMX and accelerating the transformation of free radicals). Hence, the Fe 7 S 8 -PS micro/nanocatalytic system provides a new strategy for treating highconcentration SMX-Cr(VI) cocontaminated wastewater and groundwater.